U.S. patent application number 13/450970 was filed with the patent office on 2012-10-25 for light guides.
This patent application is currently assigned to 3M Innovative Properties. Invention is credited to Gary T. Boyd, Robert Lee Erwin, Tri D. Pham, David Scott Thompson, Qingbing Wang.
Application Number | 20120268967 13/450970 |
Document ID | / |
Family ID | 47021229 |
Filed Date | 2012-10-25 |
United States Patent
Application |
20120268967 |
Kind Code |
A1 |
Wang; Qingbing ; et
al. |
October 25, 2012 |
LIGHT GUIDES
Abstract
Lightguides are disclosed. More particularly, lightguides that
include a lightguiding layer and a light extracting layer having a
structured surface are disclosed. The light guiding layer is
optically coupled to a first set of structures of the structured
surface at given locations, and is not optically coupled to a
second set of structures at given locations, thereby producing
total internal reflection at the second locations. The selective
optical coupling may be achieved by a number of different
contemplated means as discussed herein. The lightguides allow for
distribution of light along with redirection towards an image
viewer without a number of commonly required optical elements in
backlights.
Inventors: |
Wang; Qingbing; (Woodbury,
MN) ; Boyd; Gary T.; (Woodbury, MN) ; Pham;
Tri D.; (Oakdale, MN) ; Erwin; Robert Lee;
(Hudson, WI) ; Thompson; David Scott; (West
Lakeland, MN) |
Assignee: |
3M Innovative Properties
|
Family ID: |
47021229 |
Appl. No.: |
13/450970 |
Filed: |
April 19, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61478234 |
Apr 22, 2011 |
|
|
|
Current U.S.
Class: |
362/627 |
Current CPC
Class: |
G02B 6/0053 20130101;
G02B 6/0028 20130101 |
Class at
Publication: |
362/627 |
International
Class: |
F21V 8/00 20060101
F21V008/00 |
Claims
1. A lightguide comprising: a lightguiding layer comprising a first
major surface, an opposing second major surface, and a side
surface, the lightguiding layer receiving light from the side
surface, the received light propagating within the lightguiding
layer by total internal reflection from at least the first major
surface; and a structured surface facing the first major surface of
the lightguiding layer and comprising: a first plurality of first
optical structures, each first optical structure extracting light
from the lightguiding layer by frustrating total internal
reflection at the first major surface of the lightguiding layer;
and a second plurality of second optical structures, each second
optical structure not frustrating total internal reflection at the
first major surface of the lightguiding layer.
2. The lightguide of claim 1, wherein each first optical structure
frustrates total internal reflection at the first major surface by
being sufficiently close to the first major surface, and each
second optical structure does not frustrate total internal
reflection at the first major surface by being sufficiently far
from the first major surface.
3. The lightguide of claim 1, wherein each first optical structure
is taller than each second optical structure.
4. The lightguide of claim 1 further comprising an optical coupling
layer, each first optical structure frustrating total internal
reflection at the first major surface by being optically coupled to
the lightguiding layer by the optical coupling layer, each second
optical structure not frustrating total internal reflection at the
first major surface by not being optically coupled to the
lightguiding layer by the optical coupling layer.
5. The lightguide of claim 4, wherein the optical coupling layer
optically couples each first optical structure to the lightguiding
layer by adhering the first optical structure to the first major
surface, and wherein the optical coupling layer does not optically
couple each second optical structure to the lightguiding layer by
not adhering the second optical structure to the first major
surface.
6. The lightguide of claim 4, wherein the optical coupling layer is
discontinuous.
7. The lightguide of claim 4, wherein the optical coupling layer is
continuous.
8. The lightguide of claim 4, wherein the optical coupling layer is
an adhesive.
9. The lightguide of claim 4, wherein the optical coupling layer is
a pressure sensitive adhesive.
10. The lightguide of claim 4, wherein the optical coupling layer
covers the first major surface in each area corresponding to a
first optical structure and the optical coupling layer does not
cover the first major surface in each area corresponding to a
second optical structure.
11. The lightguide of claim 4, wherein the optical coupling layer
is thicker in each area corresponding to a first optical structure
and the optical coupling layer is thinner in each area
corresponding to a second optical structure.
12. The lightguide of claim 4, wherein the optical coupling layer
has a first higher index in each area corresponding to a first
optical structure and the optical coupling layer has a second lower
index in each area corresponding to a second optical structure.
13. The lightguide of claim 12, wherein the first higher index is
greater than about 1.4 and the second lower index is less than
about 1.3.
14. The lightguide of claim 1, wherein each first optical structure
frustrating total internal reflection at the first major surface by
being bonded to the first major surface by an ultrasonic welding
process.
15. A lightguide comprising: a lightguiding layer comprising a
first major surface, an opposing second major surface, and a side
surface, the lightguiding layer receiving light from the side
surface, the received light propagating within the lightguiding
layer by total internal reflection from at least the first major
surface; a light extracting layer comprising a structured major
surface facing the first major surface of the lightguiding layer,
the structured major surface comprising: a first plurality of first
optical structures, each first optical structure extracting light
from the lightguiding layer; and a second plurality of second
optical structures, each second optical structure not extracting
light from the lightguiding layer; and an optical coupling layer
adhering each first optical structure, but no second optical
structure, to the first major surface of the lightguiding
layer.
16. A lightguide comprising: a lightguiding layer comprising a
first major surface, an opposing second major surface, and a side
surface, the lightguiding layer receiving light from the side
surface, the received light propagating within the lightguiding
layer by total internal reflection from at least the first major
surface; and a structured surface facing the first major surface of
the lightguiding layer and comprising: a plurality of first linear
optical structures, each first linear optical structure extracting
light from the lightguiding layer at a plurality of first, but not
second, locations, along the length of the optical structure by
frustrating total internal reflection at the first locations on the
first major surface of the lightguiding layer.
17. The lightguide of claim 16, wherein the first locations for at
least two first linear optical structures in the first plurality of
first linear optical structures are at different locations.
18. The lightguide of claim 16 further comprising a plurality of
second linear optical structures, each second linear optical
structure not extracting light from the lightguiding layer at any
location along the length of the second linear optical
structure.
19. The lightguide of claim 16, wherein each first linear optical
structure does not frustrate total internal reflection at the first
major surface of the lightguiding layer at the second
locations.
20. The lightguide of claim 16, wherein the first linear optical
structures are taller at the first locations than at the second
locations.
21. The lightguide of claim 16, further comprising an optical
coupling layer, each first linear optical structure frustrating
total internal reflection at the first major surface at the first
locations by being optically coupled to the lightguiding layer by
the optical coupling layer.
22. The lightguide of claim 21, wherein each first linear optical
coupling layer does not frustrate total internal reflection at the
first major surface at the second locations by not being coupled to
the lightguiding layer by the optical coupling layer.
23. The lightguide of claim 21, wherein the optical coupling layer
is an adhesive.
24. The lightguide of claim 16, wherein the first linear optical
structures are bonded to the first major surface of the
lightguiding layer by ultrasonic welding.
25. The lightguide of claim 22, wherein the extraction efficiency
at the second location of the first major surface is less than
0.01%.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/478,234, filed on Apr. 22, 2011, the disclosure
of which is incorporated by reference herein in its entirety.
FIELD
[0002] The present description relates to lightguides. More
particularly, the present description relates to lightguides that
include a lightguiding layer and a light extracting layer with a
structured surface, where the light guiding layer is optically
coupled to certain structures on the structured surface at given
locations, and is not optically coupled to other structures at
second locations, thereby producing total internal reflection at
the second locations and extraction at the first locations.
BACKGROUND
[0003] Display systems, such as liquid crystal display (LCD)
systems, are used in a variety of applications and commercially
available devices such as, for example, computer monitors, personal
digital assistants (PDAs), mobile phones, miniature music players,
and thin LCD televisions. Most LCDs include a liquid crystal panel
and an extended area light source, often referred to as a
backlight, for illuminating the liquid crystal panel. Backlights
typically include one or more lamps or LEDS and may contain all or
some of the following optical components: a reflector, a lightguide
plate, bottom diffusers, crossed prism films, reflective
polarizers, diffuser cover sheets and absorptive polarizers. The
use of such a high volume of backlight components adds to both the
necessary size and cost of backlight units. It would therefore be
beneficial to provide a backlight that was capable of achieving
high-level performance without the necessity of at least some of
the components mentioned above.
SUMMARY
[0004] In one aspect, the present description relates to a
lightguide. The lightguide includes a lightguiding layer that has a
first major surface, an opposing second major surface, and a side
surface. The lightguide also includes a structured surface facing
the first major surface of the lightguiding layer. The lightguiding
layer receives light from the side surface, where the received
light propagates within the lightguiding layer by total internal
reflection from at least the first major surface. The structured
surface is made up in part of a first plurality of optical
structures, where each first optical structure extracts light from
the lightguiding layer by frustrating total internal reflection at
the first major surface of the lightguiding layer. The structured
surface is further made up in part of a second plurality of second
optical structures, each second optical structure not frustrating
total internal reflection at the first major surface of the
lightguiding layer. In at least some embodiments, the first optical
structures frustrate total internal reflection at the first major
surface by being optically coupled to the lightguiding layer by an
optical coupling layer, and the second optical structures do not
frustrate total internal reflection at the first major surface by
not being optically coupled to the lightguiding layer by the
optical coupling layer. In other embodiments, the first and second
optical structures may be at different distances from the first
major surface, such as where the first and second optical
structures have different heights.
[0005] In another aspect, the present description relates to a
lightguide. The lightguide includes a lightguiding layer, a light
extracting layer, and an optical coupling layer. The lightguiding
layer is made up in part of a first major surface, an opposing
second major surface, and a side surface, where the lightguiding
layer receives light from the side surface. The received light
propagates within the lightguiding layer by total internal
reflection from at least the first major surface. The light
extracting layer of the lightguide includes a structured major
surface facing the first major surface of the lightguiding layer.
The structured major surface includes a first plurality of first
optical structures that extract light from the lightguiding layer
and a second plurality of second optical structures that do not
extract light from the lightguiding layer. The optical coupling
layer of the lightguide adheres each first optical structure, but
no second optical structure, to the first major surface of the
lightguiding layer.
[0006] In a third aspect, the present description relates to
another lightguide. The lightguide includes a lightguiding layer
and a structured surface. The lightguiding layer has a first major
surface, an opposing second major surface, and a side surface. The
lightguiding layer receives light from the side surface, where the
received light propagates within the lightguiding layer by total
internal reflection from at least the first major surface. The
structured surface of the lightguide faces the first major surface
of the lightguiding layer. The structured surface is made up in
part of a plurality of first linear optical structures, where each
first linear optical structure extracts light from the lightguiding
layer at a plurality of first locations, but not second locations,
along the length of the optical structure by frustrating total
internal reflection at the first locations on the first major
surface of the lightguiding layer. In some cases, there may be
second linear optical structures that do not extract light at any
location along the length of the second optical structures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view of a lightguide according
to the present description.
[0008] FIG. 2 is a close-up cross-sectional view of a portion of a
lightguide.
[0009] FIG. 3 is a cross-sectional view of a lightguide according
to the present description.
[0010] FIG. 4 is a cross-sectional view of a lightguide according
to the present description.
[0011] FIG. 5 is a cross-sectional view of a lightguide according
to the present description.
[0012] FIG. 6 is a cross-sectional view of a lightguide according
to the present description.
[0013] FIG. 7 is a cross-sectional view of a lightguide according
to the present description.
[0014] FIG. 8 is a perspective view of a light extracting layer
according to the present description
[0015] FIG. 9 is a perspective view of a lightguide according to
the present description.
[0016] FIG. 10 is a perspective view of a lightguide according to
the present description.
[0017] FIG. 11 is a close-up perspective view of a lightguide
according to the present description.
[0018] FIG. 12 is a close-up perspective view of a lightguide
according to the present description.
[0019] FIG. 13 is a close-up cross-sectional view of a lightguide
according to the present description.
[0020] FIG. 14 is a cross-sectional view of a lightguide according
to the present description.
[0021] FIG. 15 is a cross-sectional view of a lightguide according
to the present description.
[0022] FIG. 16 is a cross-sectional view of a lightguide according
to the present description.
[0023] FIG. 17 is a cross-sectional view of a lightguide according
to the present description.
[0024] FIGS. 18a-d are cross-sectional views of extractor layers
according to the present description.
DETAILED DESCRIPTION
[0025] Generally, backlights utilized for display systems, such as
LCD systems, contain a wide array of different elements that are
used in combination with one another. These components may include
lighting components, such as lamps or LEDs, and other optical
components such as a reflector, a lightguide plate, bottom
diffusers, crossed prism films, reflective polarizers, diffuser
cover sheets and absorptive polarizers. The combination of all of
these components serves to provide a system that is more efficient,
with higher brightness and contrast, as well as having desired
light directionality and distribution across the viewing surface.
Unfortunately, including each of the components mentioned adds both
cost to an LCD system and volume to the backlight. It would
therefore be desirable to have a backlight that could achieve the
same performance of the backlights discussed above, while removing
at least some of the components, thereby reducing cost and device
size. Reducing the number of components, especially free-floating
components may result in less potential failure interfaces in the
backlight, such as trapped dust, or damage defects to mechanical
rubbing against a prism film. In addition, it may be desirable to
have a backlight with a standard light that could effectively
extract light without machining extraction features directly onto
or into the lightguide.
[0026] The present description provides for such a backlight. In
particular, the present description utilizes an optical film with
surface features that are optically coupled to a light-guiding
medium to extract light from that medium, and also redirect it
towards normal to the film plane (and LC panel), preferably without
the use of additional prismatic films. The present description also
allows for a standard lightguide that may effectively extract light
from a light source and guide without the need for machining
features directly onto or into the light guide. Additional
components such as a diffuser, reflective polarizer, and an
absorptive polarizer may be attached to or integrated onto the
extractor film to create a unitary light management system,
reducing the number of components in the backlight. In addition,
thinner subcomponents may be used, which as independent films would
warp or curl due to changes in environmental conditions. The
backlight system may also be attached directly to the rear
absorptive polarizer of an LCD panel, forming an entirely unitary
display with an extremely thin form factor.
[0027] The optical film of the present invention is optically
coupled to the light-guiding film in a non-contiguous manner, a
property that is important in achieving the desired lightguiding,
balance, and redirection of source light for the display. This
non-contiguous coupling may be achieved in a number of different
manners, as is described in the embodiments described
hereafter.
[0028] A first embodiment of the present description is illustrated
by lightguide 100 of FIG. 1. The lightguide 100 is made up in part
of a lightguiding layer 102. The lightguiding layer 102 includes a
plurality of surfaces. The lightguiding layer has at least a first
major surface 104 and a second major surface 106 that opposes first
major surface 104. As such, surface 106 may be understood as an
opposing second major surface. The lightguiding layer 102 further
includes a side surface 108. Side surface 108 is the location from
which light 150 is received from light source 120 and enters the
lightguiding layer to travel through the lightguide. The light
source 120 for injecting light into the lightguiding layer 102 may
include any number of conventional backlighting light sources
commonly used in the art, and further may include either one or a
plurality of light sources. In some embodiments, for example, the
light source 120 or light sources may be LED(s) or cold cathode
fluorescent lamp(s) (CCFL(s)). Lightguiding layer may generally be
made up of a solid transparent material, such as glass or a clear
polymer. In at least some embodiments, the lightguiding layer 102
may be formed by injection molding, form plating, or may simply be
a base lightguide film.
[0029] In at least some embodiments, such as that shown in FIG. 1,
the lightguiding layer 102 may be thicker near side surface 108
than at the opposing distal surface 118 of the lightguiding layer,
such that the lightguiding layer tapers to a nominal thickness near
the distal surface 118. Generally, the lightguides illustrated in
the figures of this description provide for a tapered lightguiding
layer, although this need not be the case. This tapering to a less
wide distal surface 118 allows for a thinner backlight, which is
highly desirable in flat-screen applications. Once received light
150 enters the lightguiding layer 102, it propagates within the
lightguiding layer 102 by total internal reflection from at least
the first major surface 104, as illustrated by light ray 150a of
FIG. 1. In a number of prior art backlighting applications, a
lightguiding layer such as that shown in FIG. 1 will include a
plurality of features on one or both of first major surface 104 and
second major surface 106. These features generally allow for
extraction of light by refraction, diffraction, diffusion or
reflection of light injected into the layer. In light of the
presence of these features in conventional lightguiding layers,
light generally exits what would be equivalent to the first major
surface 104 at very high angles to the surface normal. Due to the
high degree of off-axis light, such lightguiding layers require
redirection towards the normal using additional prism films and/or
diffusers, for the purpose of backlighting LCD panels. The present
description, as described above and as illustrated in FIG. 1,
eliminates the need for these further elements by extracting light
in a different manner than that conventionally shown in the prior
art. Absent extraction features on the first and/or second major
surfaces, a great deal of light 150 that travels through the
lightguiding layer 102 will be totally internally reflected, as
illustrated by ray 150a. Non-contiguous optical coupling of an
extractor film along the first major surface allows for controlled
positions and amounts of total internal reflection as well as
directionality of output light. This benefit is even more important
when considering the fact that a separate light extracting layer
may be created to effectively extract light from a lightguiding
layer that is entirely planar on a first major surface 104. This
may allow for a standard flat lightguiding layer that can be
effectively extracted from, without the necessity of machining or
etching extraction features directly onto or into the lightguiding
layer. A further description of one embodiment of the present
description is discussed below, also with respect to FIG. 1.
[0030] The lightguide 100 includes a structured surface 110 that
faces the first major surface 104 of the lightguide. The structured
surface 110 may be understood as one surface of a larger light
extracting layer 122. Light extracting layer also has a top surface
160 opposite the structured surface. The structured surface 110 is
made up of two distinct sets of optical structures. The first major
surface 110 includes a first plurality of first optical structures
112. Each of the first optical structures 112 extracts light 150b
from the lightguiding layer. This extraction is achieved by
frustrating total internal reflection at the first major surface
104 of the lightguiding layer. The first major surface also
includes a second plurality of second optical structures 114. Each
of the second optical structures 114 does not frustrate total
internal reflection at the first major surface 104 of the
lightguiding layer. For purposes of this application, and as one of
skill in the art would understand it, where total internal
reflection is frustrated, the extraction efficiency at that given
surface location of the lightguide will be close to 100%, i.e. at
least over 95%, and likely over 99% or potentially over 99.9%, and
even over 99.99%. Where total internal reflection occurs, the
extraction efficiency at that surface location is close to 0%, i.e.
less than 5%, and potentially less than 1% and even less than 0.1%
and 0.01%. It should be understood throughout this description that
although not always explicitly mentioned, first optical structures
112 (or e.g., 412, 512, 712, etc.) throughout this specification as
well as second optical structures 114 (or e.g., 414, 514, 714,
etc.) are part of a greater structure known as the light extracting
layer 122. This light extracting layer may generally be made up of
both first and second optical structures as well as a substrate or
land portion 134 that supports the structures and may offer other
functionality. Furthermore, there may be other and/or additional
mechanisms for extracting light.
[0031] Light extracting layers or films with first optical
structures 112 and second optical structures 114 may be made by any
number of methods known by those skilled in the art. These can
include, e.g. fabricating a tool using engraving, embossing, laser
ablation or lithographic methods, then employing the tool to create
the structured film/layer via cast-and-cure or extrusion
replication techniques.
[0032] A better understanding of the function of first optical
structures 112 as well as adhesive 116 in the current embodiment is
illustrated in FIG. 2. Light 150 travels through lightguiding layer
102 and at second optical structure 114 no coupling is present
between first major surface 104 and structured surface 110. Thus
light 150 is totally internally reflected at this point along the
lightguiding layer 102. However, at first major structure 112, a
coupling region is present due to the adhesive layer 116 placed
between first major surface 104 and structured surface 110. As such
light 150b is not totally internally reflected and is extracted
from first major surface into first structure 112. The shape and
angle of the structures amongst the first structures 112 is
important to the function of the device. Light 150b is not only
extracted by first structure 112 but also is incident upon facet
124 of first structure 124. Upon reflection from facet 124, light
150b is redirected at normal to first major surface 104 towards an
image panel and viewer 126. In some embodiments, light 150b may be
reflected multiple times off of facets 124 before being directed
towards a viewer 126. It should be understood that the number and
distribution of first optical structures 112 that are placed to
extract light is very important in creating the desired light
uniformity and brightness of the backlight. This allows for the
potential exclusion of, e.g., additional prismatic films, such as
brightness enhancing films.
[0033] Although FIG. 1 illustrates non-contiguous coupling of first
major surface 104 and structured surface 110 of light extracting
layer 122 by selectively patterned adhesive 116, the first optical
structures 112 may frustrate total internal reflection at the first
major surface 104 by optically coupling to the first major surface
in a plurality of other manners. A number of different contemplated
manners of non-contiguously coupling a lightguiding layer 102 to a
separate structured surface are shown in the figures and
embodiments that follow.
[0034] For example, the lightguide 300 of FIG. 3 provides a
lightguiding layer 302 that is similar to that illustrated in FIGS.
1 and 2. The lightguide also is made up in part of a light
extracting layer 322 that has a structured surface 310. Again, a
set of first optical structures 312 frustrates total internal
reflection at first major surface 304 allowing optical coupling of
light 350b. In this embodiment, the first optical structures 312
frustrate total internal reflection at the first major surface by
being sufficiently close to the first major surface 304. In a
number of embodiments, this may mean that the first optical
structures 312 are in direct contact with first major surface 304.
However, in other embodiments, the first optical structures 312 may
simply be in close enough proximity to first major surface 304 to
allow for other manners of optical coupling, e.g., evanescent
coupling. The second optical structures 314a and 314b do not
frustrate total internal reflection at the first major surface 304
by being sufficiently far from the first major surface 304. Thus
light 350a in lightguiding layer that is incident on first major
surface 304 in close proximity to second major structures is
totally internally reflected.
[0035] As will be discussed further below, in many embodiments, an
optical coupling layer may serve to couple the lightguiding layer
and light extracting layer of the presently described lightguides.
However, where no such layer is used, first optical structures
(e.g. 312) that are in close proximity to first major surface 304
may be more effectively optically coupled to first major surface by
ultrasonic welding the first optical structures 312 to surface 304
of lightguiding layer 302. Ultrasonic welding is a unique process
whereby two pieces of material are joined together seamlessly by a
solid-state weld through high-frequency acoustic vibrations.
Acoustic energy that is incident upon the two components is
converted into heat energy by friction, and the parts are welded
together nearly instantly, without any sort of adhesive or
soldering material and without any coupling layer between them at
all.
[0036] As shown in FIG. 1, the first optical structures may be in
contact with first major surface by means of a an intermediary
layer, such as adhesive layer 116 that couples first optical
structures 112 to first major surface 104 but not second optical
structures 114. However, in the embodiment in FIG. 3, the first
optical structures 312 are in close proximity to the first major
surface 304 because each of the first optical structures 312 is
taller than each second optical structure (314a and 314b). In some
cases, this may be because the second optical structure is machined
to a lower level than the first optical structures 312. An example
of one such second optical structure is element 314a. In other
embodiments, however, the second optical structure may, without any
grinding, lapping or other form of machining, be originally formed
at a lower height that first optical structures. An example of one
such structure is illustrated as element 314b.
[0037] Throughout this description, it should be understood that
the first and/or second optical structures on the structured
surface of light extracting layer may be periodically spaced in a
constant spacing manner, or may be spaced at completely different
intervals. In addition the sizes of the structures on the layer may
vary completely. FIG. 18a illustrates an embodiment in which the
structures of structured surface 1810 are spaced at a constant
spatial relation. This means that distances 1880a, 1880b and 1880c
are equal to one another. In this embodiment, the structures are
also the same size. However, the FIG. 18b embodiment is also
contemplated where although certain structures are spaced at a
common interval (e.g. distance 1880d, and 1880f) there may be a
great space between two structures 1880e. Of course, as illustrated
in FIG. 18c, varying spatial distances 1880g, 1880h, and 1880i are
also contemplated, along with varying structure sizes on surface
1810. Further, looking to FIG. 18d, adjacent microstructures (see
1812a and 1812b) may have bases that are directly adjacent and
abutting one another. In other embodiment, the adjacent
microstructures (1812c and 1812d) generally have a space between
them 1880j on surface 1820.
[0038] Looking to FIG. 4, in at least some embodiments, the
lightguide 400 may include an optical coupling layer 426. The
optical coupling layer 426 may be disposed directly on first major
surface 404 of lightguiding layer 402. In this embodiment, each
first optical structure 412 frustrates total internal reflection at
first major surface 404 by being optically coupled to the
lightguiding layer 402 by optical coupling layer 426. Each second
optical structure 414 does not frustrate total internal reflection
at the first major surface 404 by not being optically coupled to
the lightguiding layer by the optical coupling layer 426. As
discussed with the embodiment shown in FIG. 3, and with all
embodiments described herein, optical coupling between the first
optical structures 412 and optical coupling layer 426 (and by
extension first major surface 404) may be achieved by close
proximity without bonding, and potentially by evanescent coupling.
However, in many embodiments, the optical coupling layer adheres
the first optical structures 412 to the first major surface 404,
and does not adhere second optical structures 414 to the first
major surface 404. This is how the coupling and lack of coupling is
achieved in those embodiments. Thus, optical coupling layer 426 may
be an appropriate adhesive. In at least some embodiments, the
optical coupling layer may be a pressure sensitive adhesive, such
as 3M pressure-sensitive adhesive SP-7555, L4002 pressure sensitive
adhesive by KIWO, Inc (Seabrook, Tex.), or the layer may be an
adhesive cured by dry process, e.g., a UV curable adhesive, such as
optical adhesive NOA65 from Norland Products, Inc. (Cranbury,
N.J.). For further general description of potentially appropriate
adhesives for optical coupling layer 426, see A. Pocius, Adhesion
and Adhesive Technology, An Introduction, 2nd Ed., Hanser Gardner
Publications, 2002, ISBN-1-56990-319-0.
[0039] Returning to FIG. 1, the adhesive portions 116 that couple
the first optical structures 112 to first major surface 104 may
also be understood as an optical coupling layer. In another manner,
such an optical coupling layer 116 may be understood as covering
the first major surface 104 in each area corresponding to a first
optical structure 112, and not covering the first major surface 104
in each area corresponding to a second optical structure 114. In
either case, these elements 116 would be understood as a common
discontinuous optical coupling layer. Although described as an
adhesive in FIG. 1, a discontinuous optical coupling layer, as
illustrated by elements 116 may be another appropriate material
that does not act as an adhesive. Of course where a discontinuous
optical coupling layer does act to adhere first optical structures
112 to first major surfaced 104 and does not adhere second optical
structures 114 to first major surface 104, the layer may be any
appropriate adhesive, as with layer 426. In some embodiments,
adhesive 116 may be a pressure sensitive adhesive. Other
appropriate adhesive to use for layer 426 (and all other optical
coupling layers described herein) may include two part adhesives,
or resin that is post-cured by ultraviolet light or by a thermal
process. In other potential embodiments, the optical coupling layer
may be reflective at certain at certain points along the length of
the light extracting layer and transmissive at other points to
further aid in determining where light may be coupled from the
lightguiding layer to the light extracting layer.
[0040] In addition, although FIGS. 1 and 2 illustrate a
discontinuous optical coupling layer of optical elements 116, where
each first optical structure has its own corresponding discrete
coupling component, this need not be the case. For example, looking
to FIG. 6 and lightguide 600, a discontinuous layer 630a and 630b
may be split into separate portions, where at least one of the
portions (630b) optically couples multiple first optical structures
612b to first major surface 604 of lightguiding layer 602. As with
the embodiment in FIG. 1, there may be portions of discontinuous
optical coupling layer 630a that couple only one first optical
structure to first major surface 604. Where discontinuous layers
630a and 630b do not cover first major surface 604, second optical
structures 614 are not coupled to the surface and total internal
reflection within lightguiding layer 602 occurs. Although multiple
adjacent first optical structures 612b are coupled to first major
surface 604, the layers 630a and 630b may generally still be
understood as discontinuous because there are portions of major
surface 604 between the farthest reaches of layer 630a and 630b,
where no layer is present.
[0041] In another embodiment, as shown in FIG. 5, there may be a
continuous optical coupling layer 526 that optically couples first
optical structures 512 and not second optical structures 514 to the
first major surface 504 of lightguiding layer 502. However, in this
embodiment the optical coupling layer 526 has a thickness 528 in
each area corresponding to a first optical structure 512 and a
thickness 530 at each area corresponding to a second optical
structure. The thickness 528 at areas of first optical structures
is greater than the thickness 530 at positions of second optical
structures. Thickness 530 may vary at different second optical
structures 514 so long as it is less than thickness 528 and thin
enough to frustrate total internal reflection at first major
surface 504.
[0042] Another embodiment of a lightguide 700 according to the
present description is illustrated in FIG. 7. In this embodiment a
continuous, or even potentially discontinuous optical coupling
layer 732 is applied to the first major surface 704 of lightguiding
layer 702. However even where the layer 732 is continuous, as shown
in FIG. 7, portions of the layer (732a) provide for optical
coupling between first optical structures 712 and other portions of
the layer (732b) frustrate optical coupling between second optical
structures 714 by creating total internal reflection. This
selective optical coupling of a common layer may be caused by
provided a higher index of refraction in those layer portions 732a
that correspond to a first optical structure 712, and a lower index
of refraction in those layer portions 732b that correspond to a
second optical structure 714. For example the index of refraction
of layer portions 732a may be greater than 1.3, or greater than 1.4
or greater than 1.5. The index of refraction of layer portions 732b
may be less than 1.3, or less than 1.25, or potentially less than
1.2. In some cases, the layer 732 may initially be made up of a
constant or near constant index of refraction. The index may be
altered in either region 732a or 732b by patterning the layer. One
method of patterning the index is to use a patterned photo-cure
process on materials whose refractive index is sensitive to the
dosage of the cured light. An example of such a material is a
photo-refractive polymer used in making volume holograms, and ultra
low index materials whose index can be locally reduced when exposed
to light curing radiation. Examples of such materials may be found
in commonly owned and assigned U.S. Provisional Application No.
61/323941, directed towards a Patterned Gradient Polymer Film and
Method. Such patterned index materials may be attached between
adhesive layers to improve optical coupling to the lightguiding
layer or light extracting layer. Another method is to pattern low
index materials on to the lightguiding layer or light extracting
layer, followed by an overcoat of higher index adhesive material to
bond the lightguiding layer and light extracting layer (and
corresponding first optical structures).
[0043] In other embodiments, the optical coupling layer 732 may be
of uniform, or near uniform thickness, but the adhesive properties
of the layer are changed in those portions 732b to make them less
adhesive. A low adhesion area can be created by a patterning a low
adhesion coating on layer 732 by lithographic or laser ablation
methods. Areas of grater adhesion (e.g. portion 732a) can result
from UV flash exposure through an appropriate mask or focused beam
to form locally amorphous regions (e.g. 732a) on the surface that
differ in surface energy and preferentially bond in these
regions.
[0044] In any of the cases described above where an optical
coupling layer (e.g. 116, 526, 526, 630a-b, 732 and those described
hereafter) is an adhesive of some sort, it may be applied in any
number of appropriate manners. For example, adhesives may be
applied by direct placement, such as inkjet printing or screen
printing. In some embodiments, the adhesives may be patterned onto
the lightguiding layer or onto the light extracting layer's optical
structures or onto a transfer film by Laser Induced Thermal
transfer. This process includes providing a thermal transfer layer
adjacent to an adhesive layer, and placing the adhesive layer
proximate a recipient surface. A laser is then focused onto a
desired region to activate the thermal transfer material to deposit
the adhesive onto the recipient surface. Adhesives may also be
applied by a transfer process where the patterned adhesive is first
formed on a substrate with a suitable release coating, such that
after contact with the lightguiding layer or light extracting
layer, or after an ultraviolet or thermal cure process, and removal
of the substrate, the adhesive portion remains predominantly on the
desired surface. The adhesive material may be patterned on the
substrate by inkjet or screen printing, photo-lithography, or by
patterned gravure or offset printing methods.
[0045] In at least some embodiments, the structures (e.g. 112 and
114) of an extracting layer may be formed by various replication
means from tool, using UV curing, embossing, or extrusion methods,
so long as the final article is capable of transmitting light. Like
the lightguiding layer, the light extracting layer may generally be
optically clear--and thus is made of an optically clear material
such as glass or a clear polymer. However, the layer may also be
made appropriately diffuse by using particle additives or polymer
phase separation.
[0046] To this point, the lightguides in question have generally
been discussed from a cross-sectional perspective, or potentially
in a "two-dimensional" sense. It is useful to further understand
the embodiments of lightguides in the current description in three
dimensions. A perspective view of one lightguide according to the
present description is provided in FIG. 9. Lightguide 900 is made
up in part of a lightguiding layer 902 and a structured surface
910. The lightguiding layer has a first major surface 904 and a
second major surface 906 that is located opposite the first major
surface. The lightguiding layer 902 further has a side surface 908.
Input light 950 is received at side surface 908 and propagates
within the lightguiding layer by total internal reflection from at
least the first major surface 904. Ray 950a illustrates total
internal reflection at a given point on the first major surface.
The structured surface 910 is the surface of a greater extracting
layer 922. Light extracting layer 922 also has a top surface 960
opposite the structured surface 910. The structured surface 910
faces the first major surface 904 of the lightguiding layer.
[0047] In looking at the perspective view of lightguide 900, it is
clear that the embodiment illustrates not only a width of the
lightguide as was shown in previous figures, such as the distance
between a first side surface 908 and an opposing side surface 918,
but also a length 942 in the third dimension. As such the optical
structures 912 and 914 may be called "linear optical structures"
and may be understood as coupling at a given first location along
the length of the optical structure (e.g. L91), while potentially
not coupling at another given second location along the length of
the optical structure. For instance, at location L91, which is at
the very front surface of the light extracting layer, first linear
optical structures 912 extract light 950b from lightguiding layer
902. In at least some embodiments, however, at location L91, there
are certain linear optical structures that do not optically couple
to lightguiding layer 902 and thus do not frustrate total internal
reflection. This is illustrated by the distance 940a that structure
914a is positioned away from lightguiding layer at location L91,
and the distance 940b that structure 914b is positioned away from
lightguiding layer at location L91.
[0048] In at least some embodiments, the coupling status for a
given linear structure will be different at a second location along
the length 942 of the optical structure. For example, the first
linear optical structures 912 which extract light at first location
L91 are illustrated individually at location L92. At second
location L92, first linear optical structures 912a, 912b, and 912c
each do not frustrate total internal reflection. This may be due,
at least in some embodiments, to the structures being spaced away
from lightguiding layer's first major surface 904 by distances
944a, 944b, and 944c respectively. Although not required at second
location L92, in at least some embodiments, the second linear
optical structures 914 may be optically coupled to lightguiding
layer at the second location L92 as shown in FIG. 9. Therefore, at
location L92, second linear optical structures frustrate total
internal reflection and allow for light 950b to be extracted. In
this given embodiment, the coupling of the first linear optical
structures 912 at first location L1 and lack of coupling at second
location L92 is due to the fact that the first linear optical
structures 912 are taller at the first location L91 than they are
at the second location L92. In this embodiment, second optical
structures are taller at location L92, but second optical
structures need not be taller at any location along the length 942,
and may in fact be shorter.
[0049] In the embodiment shown in FIG. 9, the second linear optical
structures 914 do, at some point along the length of the structure,
provide for some optical coupling with the first major surface 904
lightguiding layer 902. However, this need not be the case. In some
embodiments, as illustrated in FIG. 10 with lightguide 1000, second
linear optical structures 1014 will not frustrate total internal
reflection at any location along the length of the second linear
optical structures. For instance at first location L101 second
linear optical structures may be spaced apart by distances 1040a
and 1040b to prevent optical coupling. At second location, L102,
the second linear optical structures may be spaced apart from the
first major surface 1004 of lightguiding layer by distances 1040c
and 1040d and at third location, L103 the second linear optical
structures 1014 may be spaced from first major surface 1004 by
distances 1040e and 1040f. The distances 1040a, b, c, d, e, and f
may be different distances or may be approximately equal or equal
distances. In any case, at these and all locations along the length
of the optical structures 1042, second linear optical structures
1014 will not extract light. In this embodiment, the first linear
optical structures 1012 may be optically coupled to first major
surface 1004 of lightguiding layer 1002 at one or all of locations
L101, L102 and L103. However, each of the three first linear
optical structures 1012 may not be optically coupled to the first
major surface 1004 at least one location along the length of the
structures 1042.
[0050] Although in FIG. 9, first optical structures share a first
location L91 where they are optically coupled to the first major
surface 904, this need not be the case. Each of the first linear
optical structures may have their own first location where optical
coupling occurs, and this first location for one given first linear
optical structure need not coincide with the first location of
another linear optical structure. A better understanding of this
may be gained by the close-up perspective view of a portion of a
light extracting film 1100. Here, first linear optical structure
1112a has first location with optical coupling at length L111.
However, first linear optical structure 1112b is not optically
coupled at length L111. Instead, first linear optical structure
1112b is optically coupled at length L112. Thus, for purposes of
this description, first linear optical structure 1112b has a first
location of optical coupling at length L112, while first linear
optical structure 1112a has a first location of optical coupling at
length L111 (or L113). Because first linear optical structure 1112a
is spaced apart by distance 1140b and 1140c at locations L112 and
L114, respectively, no optical occurs at these locations and thus
these locations cannot be considered the first location along the
length of the structures. However, at both location L113 and L111,
the structure is in contact. Thus, either location may be declared
the first location. Structure 112b is spaced apart at location
L111, L113 and L114 by distances 1140a, 1140e, and 1140d
respectively, and thus only location L112 where optical coupling
occurs can be declared the first location for the first linear
optical structure.
[0051] In FIGS. 9-11, generally the locations where coupling occurs
versus does not occur are due to the height of first and second
linear optical structures at different locations, as would
correspond to the 2-D embodiment illustrated in FIG. 3. However, as
with the 2-D embodiments illustrated elsewhere (FIGS. 1, 4, 5, 6,
etc.), the first and potentially second linear optical structures
may be selectively coupled, thereby frustrating total internal
reflection by optically coupling to an optical coupling layer. As
with the embodiments discussed above, first linear optical
structures may be optically coupled to the first major surface at a
first location, frustrating total internal reflection, and may not
frustrate total internal reflection at second locations. For
example, in the close-up view of three linear optical structures in
FIG. 12, an optical coupling layer 1250 is shown. As illustrated,
optical coupling layer frustrates total internal reflection at
first major surface 1204 by joining first linear optical structures
1212a and 1212c at that given first location L121. First linear
optical structure 1212b is not optically coupled at this location
However, at location L122 layer 1250 couples structure 1212b to
first major surface 1204. This location L122 may therefore be
declared the first location for first linear optical structure
1212b. At location L123 structures 1212b and 1212c are optically
coupled by layer 1250, while structure 1212a is not coupled to the
lightguiding layer 1204 at this location. Therefore, at location
L123 structure 1212a does not frustrate total internal reflection
at the first major surface 1204. As with the embodiments
illustrated in the 2-D perspectives, the optical coupling layer may
be any appropriate material. In at least some embodiments, the
layer 1250 will be an adhesive, such as a pressure sensitive
adhesive, or alternatives discussed further above.
[0052] It should further be understood that in looking at FIG. 12,
one may understand such a figure to correspond to a potential
3-dimensional version of the embodiment shown in FIG. 1. As such,
other potential adhesive layers, both continuous and non-continuous
are contemplated. For example, the adhesive layer 1250 of FIG. 12
may be continuous across the width 1290 of the lightguiding layer
as in FIG. 4, such that structures 1212a, 1212b, and 1212c do not
couple at positions where they have a lower height (e.g. in FIG.
11). Elsewhere, coupling layer 1250 may be continuous and of
different thicknesses, as shown in 2-dimensions with FIG. 5, such
that it bonds with optical structures 1212a, 1212b, and 1212c at
length locations and at points along the width of the lightguiding
layer where the layer 1250 is thick enough to come into contact and
couple with first optical structures. Selective coupling by
different refractive indices within a common coupling layer 1250,
as shown in FIG. 7 are also contemplated in this 3-dimensional
embodiment. The variations may simply occur not only across the
width 1290 of the lightguiding layer, as shown in 2 dimensions, but
also along the length (see 1042 of FIG. 10) of the optical
structures and lightguiding layer.
[0053] Looking to FIG. 8, it is important to note that where
understood in 3-dimensions, the first linear optical structures
(e.g. 812) and second linear optical structures (e.g. 814) may be
understood as potentially varying in height, but also being
continuous along the length of the light extracting layer 842. As
such, the length of the structures is far greater than the base
width 855 of such structures. For example, the ratio of the length
of the structures (along length of film 842) may generally have a
ratio over the width of base 855 of at least 10, or at least 50, or
at least 100, or at least 500, or at least 1000. In addition, the
first and second optical may have a constant height 850, as with
first optical structure shown here 812, or may have a varying
height such that portions are taller (e.g. height 860a) and shorter
(e.g. height 860b). However, the height of such structures will
generally not be understood as going to zero along the length of
the film 842. Thus, while the layer 822 may have discontinuous
discrete structures along the width of the layer 890, the
structures will be continuous, although potentially of varying
heights greater than zero, along the length 842.
[0054] At this point, discussion may, for ease of description,
refer to 2-D illustrations showing further embodiments of the
current specification. However, it should be understood that for
any further discussion and characterization of "first optical
structures" and "second optical structures" in 2-D embodiments, the
same characterization should be understood to apply as equally
effective with respect to "first linear optical structures" and
"second linear optical structures."
[0055] Returning to FIG. 1, the tip of the first and second optical
structures may have a substantially flat face parallel to the plane
of the light extracting layer 122 and/or lightguiding layer 102. In
nearly all the figures the first and second optical structures or
linear optical structures are illustrated with flat faces parallel
to the plane of the film(s). However, in some embodiments, the face
may have a fine surface structure. Such an embodiment is
illustrated n FIG. 13. Fine surface features 150 may serve the
purpose of minimizing optical contact with the lightguiding layer
102 in regions where there is no coupling layer (such as an
adhesive 116), i.e. in FIG. 1, below second optical structures 114.
Minimizing surface contact and providing directional structure may
diffuse any light leaked from the lightguiding layer 102. Methods
to create fine surface features 150 include chemical etching or
plating of a micro-replication tool, utilization of fine structured
diamonds in the original tooling process, post patterning of the
tool surface by mechanical means (e.g. sanding), or post processing
of the replicated structured surface by laser ablation or
mechanical means.
[0056] It is important to note that the first and second optical
structures need not have a flat surface to contact the adhesive
that creates optical contact with the lightguiding layer (where an
adhesive is used). Rather, the tips of the structures may be
pointed, truncated, or roughened, and these tips will be
substantially index matched by the adhesive, effectively truncating
them from an optical viewpoint. Any index mismatch between the
structures and the adhesive (where used) can be used to mitigate
the angle and spatial distribution of the light advantageously.
[0057] Although the present description provides for a lightguide
in which a number of supplementary optical components generally
used for backlighting may not be necessary, the lightguide may also
be used in conjunction with other optical elements. For example,
light may be optically diffused following extraction by the light
extracting layer. Methods to combine a diffuser with a light
extracting layer (e.g. layer 122 or 922) include using replicated
surface structure on the top surface of the light extracting layer
(opposite the structured surface--see, e.g., 160 or 960), using
diffusive particles within the light extracting layer, or
potentially applying a diffusive coating on the top surface of the
light extracting layer. Alternatively, a substrate for the light
extracting layer can be diffusive.
[0058] FIG. 14 illustrates another contemplated embodiment of the
present description. A reflective polarizer may be incorporated
with the light extracting layer by microreplicating the first and
second optical structures 1412 and 1414 directly on to reflective
polarizer films. The reflective polarizer 1401 serves to increase
backlight brightness by recycling polarized light. A reflective
polarizer for use with the light extracting layers currently
described may be multi-layer, wire grid, or cholesteric type.
Examples of suitable reflective polarizers include 3M Dual
Brightness Enhancing Film, cholesteric, and wire grid films or
plates. Another example is Collimating Multilayer Optical Film or
CMOR, which has both polarization and angle recycling capabilities.
Looking to FIG. 15, a diffuser function may also be incorporated
into the adhesive 1503 that joins the light extraction structures
and the reflective polarizer. The combination of a lightguiding
layer 1502, an extracting layer 1522, a diffusive adhesive 1503 and
a reflective polarizer 1501 allows for an extremely thin and
efficient unitary backlight construction.
[0059] Another potential contemplated element to be used in
conjunction with the lightguides described herein is illustrated in
FIG. 16. A reflector 1660 may be incorporated into a unitary
backlight construction with lightguiding layer 1602 by adhering it
to the second major surface 1606 (or lower surface) of lightguiding
layer 1602 opposite first major surface 1604 (and light extracting
layer 1622). Methods of adhesion include lamination by a spatially
uniform adhesive, lamination using a patterned adhesive or low
surface area adhesive, such as a microsphere adhesive. It may be
advantageous to use adhesive with an effective refractive index
(refractive index of adhesive+that of air) which is lower than that
of the lightguiding layer in order to facilitate light guiding.
Generally, the first optical structures' distribution will depend
on this effective index to maximize backlight efficiency and
uniformity.
[0060] Another potential component that may be used in conjunction
with the lightguides of the present description, or as part of the
lightguides of the present description, is an angle management film
1770. As illustrated in FIG. 17 an angle management film may be
adhered to the top of the extracting layer or film 1722, in order
to better redirect light along the width of the lightguide and
lightguiding layer 1702. One example of a suitable angle management
film 1770 would be a brightness enhancing film, such as BEF from 3M
Company, whose prisms run along the length of the 3-D lightguide
(e.g. 942 of FIG. 9). Another suitable angle management film would
be a layer of microbeads or other suitable prismatic structure. The
reflective polarizer 1401 or 1501 provided in FIGS. 14 and 15 could
be placed between the extracting layer 1722 and the angle
management film 1770, can be adhered to the top of the angle
management film (1772), or may be separate from the construction.
In the case of linear prismatic structures, an extended tip may be
used for enhancement of adhesion to a top film, with minimal impact
on the air space needed to achieve best performance. A diffusive
element such as the potential embodiment provided above (e.g. a
diffusive coating, diffusive adhesive, diffusive particles in light
extracting layer 122, etc.) may also be included in the embodiment
of FIG. 17 to improve spatial uniformity. Preferably the diffusive
element will be included on the opposite side of the reflective
polarizing element from the image display. For example, a diffuse
adhesive 1703, such as diffuse adhesive 1503 in FIG. 15, may be
used to laminate the light extracting layer 1722 to a reflective
polarizer, or a reflective polarizer to angle management film 1770,
or an extracting layer 1722 to management film 1770 (as illustrated
in FIG. 17).
[0061] In a case where a reflective polarizer is placed between a
light extracting layer (e.g. 1722 of FIG. 17) and an angle
management film (e.g. 1770 of FIG. 17), the reflective polarizer's
pass axis may be placed at an arbitrary orientation to the
extractor and angle management film axes. For example, a reflective
polarizer may be laminated to the top of the extractor layer at a
desired orientation followed by lamination of the angle management
film at an angle crossed (90 degrees) to that of the extraction
film. Another method of manufacturing the combination of extractor
layer, reflective polarizer and angle management film is to use
rotated tooling for both the extractor layer and angle management
film, and replicate these features onto respective sides of the
reflective polarizer, either in a sequential or parallel
replication process.
[0062] The unitary backlight component described above (and one or
all of the additional components discussed) may also be attached to
the lower absorptive polarizer of an LCD panel. An advantage of
this construction is to provide structural integrity to the
backlight elements, and to simplify system design. The attachment
adhesive for the elements may again be used to diffuse light and
improve backlight illumination uniformity.
[0063] The spatial uniformity of the backlight system consisting of
a lightguiding layer and a light extracting layer may be adjusted
by suitable patterning of the extracting layer structure
distribution, the coupling medium, or a combination of the two, as
described herein. In addition, the lightguiding layer may be
modified by applying an extractor or diffusive layer on the second
major surface (e.g. surface 106 of FIG. 1) to fine tune the degree
of uniformity afforded by the lightguiding layer (102) and its
associated coupling.
[0064] To maintain uniformity of the light outputted from the
display, it also may be desirable to have light extracting optical
structures that are further away from the light source be greater
in size, and more closely positioned. Light extracting optical
structures that are closer to the light source may generally be
smaller in dimension and potentially spaced further apart.
[0065] The present invention should not be considered limited to
the particular examples and embodiment described above, as such
embodiments are described in detail above to facilitate explanation
of various aspects of the invention. Rather, the present invention
should be understood to cover all aspects of the invention,
including various modifications, equivalent processes, and
alternative devices falling within the spirit and scope of the
invention as defined by the appended claims.
* * * * *